I've had exactly the same problems with a brand-new Vigor 120 (V120_322_321311 firmware) - it drops the connection at random but re-syncs quickly.

The same line is completely stable when I use a Vigor 100 on it.

I have also noticed that the Vigor 100 is more consistent in terms of downstream sync speed (constantly at 7616000) but the 120 varies a fair bit (7392000 to 7616000), AND the loop attenuation is 6-7db higher when the Vigor 120 is connected.

I've now applied the official 3.2.4 firmware to my Vigor 120 - and it is a huge improvement.

Before the upgrade, it didn't manage to stay up for more than a few hours at a time, but so far it has been running for 44 hours without a single disconnection. Downstream/upstream speed, SNR and attenuation seem to be stable, and the figures are pretty much the same as I'd expect to see from my old Vigor 100.

My BRAS profile dropped from 6500 to 6000 but I did mess up the switchover and bounced my line about a bit - it will be interesting to see if it returns to 6500 in the next couple of days. Before the firmware upgrade, the Vigor 120 disconnected so often that I was busted down to a 5000 profile for a while !

The jury's still out for long-term stability, but so far 3.2.4 looks to have nailed most of the bugs I saw with 3.2.1/3.2.2.

Have just applied 3.2.4 as having exactly same issue. Speed was dropping from so many disconnects and already back up from 6Meg to more usual 12 via Talktalk. Lets hope this fixes the problem of otherwise fine new router